This invention relates to the refinement of high quality precious metals and consisting of silver and gold from ore or scrap or other such precious metal-bearing metallic materials that effectively and quickly removes base metals such as copper, zinc, iron or lead to produce a high quality bullion containing more than 99.9% of such precious metal, while enhancing the overall amount of such recovered precious metal.
Since the discovery and introduction of gold and silver, into society, man has constantly sought ways of increasing the efficiency of refining techniques which includes reducing the refining time without diminishment of purity levels, while increasing the amount of recovered metal. The escalation in value (price per ounce) of silver and gold in recent years, intensifies the need for an efficient refining process for precious metals having a low turnaround time at the refinery. Since gold and silver often form the basis of currencies, each day of processing time can represent substantial monetary losses to the owner of the precious metal-bearing materials. Unrecoverable precious metal lost in refining also represents a substantial economic loss. Other considerations, especially environmental, add additional costs to refining. Finally increased energy costs also result in increased refining costs.
In spite of the recent events and problems with respect to the spiraling costs of refining high quality (99.5%) precious metals, present day commercial refining of silver and gold employs electrolytic refining techniques (used for over half a century). The primary deficiencies with electrolytic refining of precious metals is that it (1) results in high losses of the precious metal during refinement that cannot be recovered; (2) requires the use of acids which increase handling and disposal problems and costs; (3) introduces acidic and corrosive fumes during the refining process which require fume control techniques such as venting and the like; (4) consumes large amounts of energy and requires costly equipment; and (5) presents unnecessary health hazards for employees.
Methods of refining precious metals disclosed in the prior art clearly document the problems discussed above. In U.S. Pat. No. 1,004,576 issued to Neilly, Oct. 3, 1911, a process is described for refining silver that includes first making a "speiss" which introduces more base metals, and concludes with an air blast technique, the entire process consuming a long time period. In U.S. Pat. No. 3,902,890, a method is employed for refining silver-bearing residues that includes three successive furnace processes, low purity levels (86%) and is very slow (30 hours per batch). In Kapanen et al, U.S. Pat. No. 4,029,494, a method of recovering noble metals is employed that requires a long time period and additional refining to obtain bullion quality.
The present invention provides a method of obtaining high quality (bullion) silver or gold using a pyrotechnical refining process that greatly reduces refining time and high loss of material, eliminates the handling and disposal problems of acids and fume control and reduces the energy costs and complex equipment required.